Mergers, Acquisitions and Dispositions - Pro Forma Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Total revenues	$ 38,245	$ 38,556	$ 38,819	$ 37,946	$ 14,300	$ 11,457	$ 11,480	$ 11,413	$ 153,566	$ 48,650	$ 41,806
Shareholder's net income	$ 977	$ 1,351	$ 1,408	$ 1,368	$ 144	$ 772	$ 806	$ 915	$ 5,104	2,637	2,237
Express Scripts Holding Company [Member]
Business Acquisition [Line Items]
Total revenues										2,600
Shareholder's net income
Express Scripts Holding Company [Member]
Unaudited pro forma information [Abstract]
Pro forma total revenues										149,544	143,288
Pro forma shareholders' net income										$ 5,632	4,435
Transaction-related costs included in pro forma shareholders' net income											$ 1,200